1. Field of the Invention
This invention relates to a guide roll apparatus for a dryer of a paper machine drying section. More specifically, this invention relates to a guide roll apparatus in which the web and a web-supporting felt disposed contiguous relative to each other are guided through the drying section of a papermaking machine.
2. Information Disclosure Statement
For many years, so-called "serpentine run" or "uno-run" drying sections have been employed by papermakers in order to dry the formed web emerging from a press section of the papermaking machine. Such serpentine type drying sections typically included an upper and a lower line of dryer drums and the web to be dried would successively move supported by a felt between alternate upper and lower dryer drums. Although the aforementioned serpentine run has been extensively employed, such arrangement has certain inherent disadvantages. For example, when both the upper and lower line of dryer drums are heated, the web comes into physical contact only with the heated dryer drums of the upper line of dryers because only the felt comes into direct contact with each of the dryer drums of the lower line. In operation of such serpentine drying sections, the application of heat to the lower line of dryers has, to a large extent, been ineffective due the heat-insulating effect of the drying felt disposed between the surface of each lower drying drum and the supported web. In view of the resultant wastage of heating steam and the relatively costly requirement for such lower line of dryer drums, such lower line of drums have recently been replaced by guide rolls (or transfer rolls) disposed between each adjacent upper dryer drum. Throughout this specification, the term "guide roll" is intended to include transfer rolls for transferring the web between adjacent dryers or grooved vacuum rolls. This so-called "Bel Run" arrangement with guide rolls disposed between adjacent upper drying drums, has reduced the steam requirements compared with the aforementioned serpentine run arrangement. Also, such guide rolls are smaller and generally less costly than the corresponding lower dryer drums. Furthermore, due to the smaller size of the guide rolls, the draw, or length of the felt, between an upper dryer drum and a respective guide roll is considerably reduced compared with the serpentine run thereby avoiding, to a large degree, problems arising from the edges of the web fluttering when operating at high production rates of 3,000 fpm or more. Another advantage of the Bel Run system is that the overall height of the Bel Run is less than the height of a serpentine run.
With the ever-increasing production speeds of papermaking machines, however, it is not uncommon to operate dryer sections of the Bel Run type in excess of 4,000 fpm. At such speeds, even with the relatively short draw between the guide roll and associated dryer drum, there exists a tendency for the edges of the web to lift and flutter relative to the supporting felt as the contiguous felt and web extend around and wrap a portion of the guide roll.
In the prior art, various types of vacuum rolls have been employed in an attempt to adequately draw the web, and particularly the web edges, into close conformity with the supporting felt. However, such vacuum rolls are relatively costly to manufacture, such cost approaching the cost of the manufacture of a corresponding lower dryer drum of a serpentine run system.
The present invention provides a greatly simplified type of guide roll which avoids the complex structure of the aforementioned vacuum rolls used previously.
The present invention, essentially, includes a guide roll having a plurality of spaced, circumferential grooves defined by the external surface of the guide roll such that as the felt and web wrap around the guide roll, the buildup of air pressure at the ingoing nip defined by the felt and the guide roll, is dissipated through the plurality of channels, or grooves.
More specifically, the present invention includes a guide roll in which the edge portions of the guide roll have a plurality of spaced, circumferential grooves in combination with a vacuum hood, or vacuum inducing device, disposed in the pocket formed by the ingoing and outgoing felt and the guide roll such that the buildup of pressure at the ingoing nip is drawn away from this nip through the grooves towards the vacuum hood.
Alternately, the present invention accomplishes the same purpose by providing a hollow guide roll defining a plurality of radially-extending holes disposed adjacent to the respective edge portions of the roll. A partial vacuum is applied to the hollow roll through one or more journals of the roll such that in use, the air pressure built up between the felt and the edge portions of the roll is drawn away through the holes towards the vacuum, and additionally, vacuum support is provided directly to the web edges as they wrap around the guide roll.
Therefore, it is a primary object of the present invention to overcome the aforementioned complexity and cost factors involved with the prior art guide rolls and to provide a guide roll apparatus that offers a significant contribution to the art of drying paper webs in a papermaking machine.
Another object of the present invention is the provision of a guide roll apparatus in which a first and second edge portion of a guide roll defines a plurality of spaced, circumferential grooves such that in use of the apparatus, the buildup of pressure at the ingoing nip is dissipated through the grooves towards a vacuum hood disposed within a pocket defined by the ingoing and outgoing felt and the guide roll.
Another object of the present invention is the provision of a guide roll apparatus which includes a hollow guide roll having radial holes disposed adjacent the respective side edges of the roll. Vacuum is applied through the hollow guide roll such that in use, the buildup of air pressure between the felt and particularly the edge portions of the guide roll is dissipated through the holes towards the vacuum.
Another object of the present invention is the provision of a guide roll in which the hollow guide roll includes a divider plate for dividing an enclosure of the hollow guide roll into a first and second enclosure with the first and second enclosure being, respectively, in communication with the holes of the first and second edge portions.
Another object of the present invention is the provision of a guide roll apparatus in which the divider plate defines a restrictor opening such that a greater vacuum is applied to one edge portion than to the other edge portion. This greater vacuum is used when threading a tail of a web so that loss of vacuum through the remaining unwrapped edge portion is inhibited.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the following detailed description of the preferred embodiment of the present invention taken in conjunction with the annexed drawings.